The pretty good entry Visual Novel: Katawa Shoujo

Traffic Department 2192  (released as freeware by author in 2007)

Traffic Department 2192

Top down vehicle shooter with a surprisingly mature story for it's time, I would recommend it for the story alone as it keeps a good pace and the characters are very fleshed out and believable.

Abandonia.com has a huge pile of free games. It is legal, as well. As soon as one of the games on the sight gets added to GoG and stuff like that, the downloads gets removed.

Sango Fighter

A decent Street Fighter clone set in Ancient China with a few unique game mechanics and a diverse move set (controller recommended) game was made freeware in 2009.

Beneath a Steel Sky is definitely one that gets my recommendation. Loved it quite a bit when I went through it around 10 years ago.

Ultima IV is free on GoG, I think. One of the best rpgs ever made, BUT it looks dated. Very, very dated.

Marathon Trilogy

Available for Windows, Mac, and Linux

This is an open Source remaster version.

This is one hell of a triple pack, really. I remember playing the first one on a Snes emulator (I think it was). It plays a bit like Flashback, if you remember that gem of a game.

The second one - Lost Vikings, I played loads when it came out in the 90s. A very unique game at its time, and incredibly well designed. I think my sister actually beat it. Kudos to her if she did that before the internet and walkthroughs etc.

The third one I remember very well. I think it was early summer in...2002 or something. Me and two friends played that one and a few others all day for weeks. Snes emulator that time as well. Racing games are always better when you can bump other players off the road, or destroy them with weapons.

SPACE ELVIS??!!

IN!!